Process for removing accumulated matter in pipes by means of a heated travelling element

Abstract: A process which consists in introducing inside a pipe (1) which carries substances which eventually leave a meltable residue, a cylindrical travelling element or pig (2) made of low density high elasticity foam having added to its body, for example packed in cavities or soaked within its pores, a mixture of reagents (3) which after a certain period of time will cause a highly exothermic reaction to occur so that by displacing the pig (2) past the meltable residue within pipe (1), said residue will melt and will be carried to a place from which they will be removed together with the pig.

Description: This invention concerns a process for removing from inside a pipe accumulated matter which can be melted to be later dragged by a travelling element moving inside the pipe. It applies specifically to the use of a polymeric cylindrical element driven by a fluid flowing in the pipe. This travelling element (from now on referred to as a pig) is heated either by means of a chemical reaction or through a physical-chemical effect. Inside a pipe in which there is a flow of liquid products, deposits are created which reduce the effective liquid flow area and cause problems for the flow. These problems are all the more serious when the flow through these pipes is of crude oil or its refined products often over large distances. To remove or to clean such debris it is very common to introduce, at a certain point, an object or device (named a pig) which fits the pipe internal dimensions. This pig is moved by the fluid (liquid or gas) pressure, flowing (preferably at a high speed) and dragging (scraping) the deposit to a place in which it is removed together with the "travelling" object. However, such a process presents certain drawbacks concerning the shape and constitution of the "travelling" device. One of the most serious drawbacks is the lack of clearance between the device and the inner pipe walls, as the device (or pig) is designed to scrape these walls in its movement with a risk of becoming jammed or destroyed. These problems may require the pipe disassembly for the removal of the pig. More recently pigs or scrapers have been designed which are made of a polymeric foam which is of very low density as compared to the existing foams. This can be seen in EP-A-0581616. Besides being of reduced costs, such a pig can be introduced and driven along pipes subject to large diameter variations, thanks to its large elasticity and wear resistance. In the case of paraffinic oils, when there is a paraffinic wax accumulation on the walls, it would appear as an immediate solution to the operators of the pipe (or, more specifically an oil pipeline) to cause melting of the deposit by means of a local heating. However, to succeed in heating such a pipe is sometimes not an easy task since, in general, one is dealing with pipes of considerable extent in which the accumulation points are not easily accessible. The prior art has made very little progress in this field, except in very few cases of electrical heating at points of easy access and, even so, in pipes of small extent, although not covering the specific pipeline case. So basically in the prior art the attempt to remove the accumulated deposit in pipes has concentrated on the strong mechanical action of highly abrasive scrapers of rather complicated designs, including brushes or bristles of high strength, or even scrapers made of metal, as is known in the art. The process of the present invention can be applied to "in situ" heating of deposits (specially paraffinic wax) that can be made to melt, and to their later dragging by means of a pig. The polymeric foam pigs (made of low density, high elasticity polyurethane as described in the above EP-A-0581616) have solved this problem, as these pigs are deformed by the impelling fluid pressure and are able to take the shape of the inner surface of the pipe. The present invention is characterised by the features of claim 1. The pigs referred to above made of polymeric foam, can behave as carriers of chemical substances which, through their reaction or under the effect of certain physical-chemical processes, cause local heating at critical points where a plug is formed due to the accumulation of organic solid meltable deposits. The objectives of the invention will be more readily perceived from the following detailed description given with reference to the accompanying drawings, in which: FIGURE 1 shows a simplified sectional view of a simple pig, carrying the components that will cause heating and the ensuing cleaning; FIGURE 2 shows, also in a sectional view, another product similar to that of Figure 1, but introducing a cleaning auxiliary pig following the first one; and FIGURE 3 shows a more complex embodiment based on that shown in Figure 1, but provided with means for coping with cases of more severe deposits. Referring to Figure 1, there can be seen a nearly cylindrical pig made of a low density and a high elasticity foam, with a cylindrical internal cavity in which there is a mixture which will cause a highly exothermic reaction to occur. In operation the reagent 3 is put inside the cavity of pig 2, and the pig is then put inside the pipe 1 to move therealong while pressure is applied by the fluid flowing behind the pig. In view of its already mentioned resiliency characteristic the foam is deformed to fit perfectly well into the internal wall dimensions while the reaction of the chemical reagent 3 contained in the cavity 2 produces a strong heating effect. If there is no blockage in the pipe, the heat generated will be dissipated during the long path of the pig 2 along the pipe. If there is any retention of the pig caused by the accumulation of an undesirable deposit of meltable material, the pig 2 will stop moving or will reduce its speed, thereby concentrating the released heat at the location of the plugging deposit. After a certain time, the plugging deposit will become molten, freeing the way for the pig to resume its passage, as the flowing driving fluid continues to exert pressure on the back of the pig. Considering that the pig is a perfect fit in the pipe (due to the properties of the material of which the pig is made), there will be a momentary blocking, with the resultant increase in pressure releasing the pig and dragging the plugging material which has been made molten by the action of the heat. The reason for that is that the pig is highly elastic, as demonstrated in practical applications, so due to its manufacture the pig itself cannot become retained indefinitely. In Figure 2 the cavity (or "bag"), where the reagents 3 are that will react to produce heat inside the pig 2, is of annular shape, being in this case intended for the use of reagent mixtures of large heat capacity. As can be seen, this is recommended when the material to be removed requires a more intense heat application. In this case, a conventional scraper 4 will be introduced inside the pipe behind the plastic pig 2. This scraper 4, the design of which is not defined here, will aid in the removal of the undesirable deposited material displaced by melting. As suggested hereinbefore this approach is designed for the most difficult cases in which the pig efficacy alone is not sufficient for the desired removal, and due to the pig's resiliency characteristics that prevent its retention in the pipe, the amount of the material displaced cannot be removed in one single pig pass. Figure 3 shows an embodiment which aims at first to remove the meltable plugging material (e.g. paraffin wax) along large extents. In this case, the reagents 3 which produce the exothermic reaction are soaked in the interior pores of the pig 2. Behind the pig 2 is an area which constitutes an actual piston (or bed) of chemical material 5 which can either dissolve the molten plugging material chemically or produce a release of heat for example upon contact with the reagent 3. This is followed by a conventional scraper 4. Here, backing the pig as the main element, is a pipe cleaning "train" formed in a manner similar to that of gelled piston trains. As for the heating-producing reagent, there are several specialized chemical aspects to be recommended, but the choice is highly dependent on the nature of the product material normally carried in the pipe, as well as on the local availability. So, among the possibilities there can be mentioned, while not in any way constraining the present application:-the reaction of an ammonium salt with a nitrite, reacting an isocyanate with a foam-forming component, a catalytic reaction between a phenol and an aldehyde, water addition for dissolution of calcium chloride or zinc chloride, the reaction of water with calcium oxide to form dead lime, and others. If there is a possibility of immediately putting reagents in the pipe and beginning the displacement of the pig, the contact between the components can be made definitely when they are introduced in the pig cavity. If any travel time is predicted before the beginning of the exothermic reaction, the components could stay side-by-side in separate and conditioned containers, (e.g. in plastic bags), which are easy to be discarded and will be ruptured when the pressure becomes abnormally high as when plugging arises, thus starting the exothermic reaction. The details given above should not be construed as a limitation of our process, but rather it is a hint to the experts regarding one embodiment of the invention.

Claims: A process for removing accumulated deposits in pipes by means of a travelling element, said travelling element being a scraper or cylindrical pig (2) made of a low density, high elasticity polymeric foam; characterised by adding to said pig (2) reagents which, by chemical reaction or physical-chemical modification cause a highly exothermic reaction; immediately afterwards introducing the pig together with the reagent into a pipe (1); and causing the displacement of said pig (2) by means of a flowing fluid so that, by displacement of the pig, the reagents added to the pig are reacted and generate heat so that, as said pig (2) passes by a meltable deposit accumulated within said pipe (1), the heat of reaction causes the melting of the deposit and carries it to an opening of the pipe (1) wherefrom pig and deposit are taken out. A process according to claim 1, wherein the reagents (3) are placed inside a cylindrical cavity within the pig (2). A process according to claim 2, wherein the reagents (3) are added inside an annular cylindrical cavity in the body of the pig (2). A process according to either of claims 2 and 3, wherein the reagents are packed in containers which are easily ruptured by pressure at the moment they are introduced in the cavity of the pig (2). A process according to claim 1, wherein the reagents (3) are soaked within pores of the body of the pig (2). A process according to any one of claims 1 to 5, wherein a standard scraper pig (4) is introduced immediately after the pig (2) which contains the reagents (3) causing the exothermic reaction. A process according to claim 6, wherein before the standard scraper pig (4) is introduced in the pipe but after the introduction of the pig (2) which contains reagents (3), an intermediate bed (5) is introduced which is made up of chemical reagents which together with the other elements constitute a cleaning train. A process according to any of claims 2 to 5, wherein the reagents which are to be brought into contact are previously mixed at the very moment of their placement inside the cavity of the pig (2) and of the placement of said pig (2) inside the pipe (1) for the displacement of the pig (2) throughout the pipe.

Inventors: DACIER LABATO CARMEN SILVIA DI, LIMA PAULO CEASAR RIBEIRO, SALIBA CARLOS ALBERTO MATTOS, DACIER LABATO, CARMEN SILVIA DIAS, LIMA, PAULO CEASAR RIBEIRO, SALIBA, CARLOS ALBERTO MATTOS
Applicants: PETROLEO BRASILEIRO SA, PETROLEO BRASILEIRO S.A. - PETROBRAS
Application year: 1994
Main classification: B08B9
IPC codes: B08B9